Iron-comprising heterogeneous catalyst and process for preparing olefins by reaction of carbon monoxide with hydrogen

ABSTRACT

Iron-comprising heterogeneous catalyst and a process for producing it, which comprises the steps of thermal decomposition of gaseous iron pentacarbonyl to give carbonyl iron powder having spherical primary particles, treatment of carbonyl iron powder with hydrogen, resulting in the metallic spherical primary particles at least partially forming agglomerates, contacting the agglomerates with iron pentacarbonyl, and thermal decomposition of the iron pentacarbonyl to give at least predominantly pore-free and void-free secondary particles.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of European patent application no.09175218.8 filed Nov. 6, 2009, the contents of which are incorporatedherein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to an iron-comprising heterogeneouscatalyst, a process for producing it and a process for preparing olefinsby reaction of carbon monoxide with hydrogen in the presence of theiron-comprising heterogeneous catalyst.

BACKGROUND OF THE INVENTION

It is known that lower olefins can be prepared from carbon monoxide (CO)and hydrogen (H₂) over metal catalysts, e.g. iron or cobalt catalysts.Iron oxides are usually used as catalyst precursors. Such catalysts aredescribed, for example, in U.S. Pat. Nos. 4,544,674, 5,100,856,5,118,715, 5,248,701, US 2004/0127582 A1, H. P. Withers et al., Ind.Eng. Chem. Res. 1990, 29, pages 1807 to 1814, and M. E. Dry et al.,Stud. Surf. Sci. Catal., Vol. 152, 2004, pages 533 to 600.

This reaction is also referred to as the Fischer-Tropsch synthesis.

Conventional processes for the Fischer-Tropsch synthesis producehydrocarbons in a wide range of product distribution.

This range of product distribution can basically be characterized by theAnderson-Schulz-Flory distribution; cf. also: M. Janardanarao, Ind. Eng.Chem. Res. 1990, 29, pages 1735-53.

It is likewise known that the composition of the hydrocarbons formed inthe Fischer-Tropsch process can be strongly influenced by the choice ofthe catalysts used, the reactor types and the reaction conditions.

For example, it is known that the product distribution can be shifted inthe direction of lower olefins by use of high temperatures in thepresence of modified iron catalysts: B. Büssemeier et al., HydrocarbonProcessing, November 1976, pages 105 to 112.

The main problem here is the formation of large amounts of undesirablemethane (CH₄).

In addition, the iron oxides required as starting material for thecatalyst are difficult to reduce.

DE 28 22 656 A1 (Inst. Fr. du Petrole) discloses a Fischer-Tropschprocess in which the catalyst is obtained by deposition of ametal-organic iron and/or cobalt and/or nickel aggregate onto aninorganic support. The deposition of the aggregate on the support iseffected by impregnating the support with a solution of the aggregate.This process is said to form C2-C4-olefins (“lower olefins”) selectivelyand only small amounts of methane are said to be formed. The maindisadvantage of these catalysts is that the active catalyst constituentscan be volatile under the reaction conditions, which means a loss ofmetal, and that they are toxic.

DE 29 19 921 A1 (Vielstich et al.) describes a further Fischer-Tropschprocess in which catalysts comprising polycrystalline iron whiskers assubstantial catalyst component are used. These iron whiskers areobtained by thermal decomposition of iron pentacarbonyl in a magneticfield. The iron whiskers are preferably used as pellets. According tothe teaching of this DE document, polycrystalline whiskers are fine ironthreads having microscopically small single crystal regions (page 5, 3rdparagraph). The thread-like primary particles gain their shape fromgrowth in a magnetic field. The threads have a length of, for example,from 0.06 to 1 mm.

The two pictures in “Fachberichte für Oberflächentechnik”, July/August1970, page 146, show scanning electron micrographs of such a carbonyliron powder having thread-like primary particles.

“Fachberichte für Oberflächentechnik”, July/August 1970, pages 145 to150, also describes these iron whiskers as metal hairs which result fromcrystal growth of the metal in thread form, unlike normal crystal growth(page 145, 2nd paragraph). In the polycrystalline iron whiskers, theratio of length to diameter is, for example, ≧10.

Such polycrystalline iron whiskers are also described in H. G. F.Wilsdorf et al., Z. Metallkde. 69 (11), 1978, pages 701 to 705.

DE 25 07 647 A1 (Köbel et al.) describes the use of catalysts comprisingmanganese and optionally iron for preparing hydrocarbons andoxygen-comprising compounds from CO and H₂.

U.S. Pat. No. 2,417,164 (Standard Oil Comp.) relates to processes forsynthesizing liquid hydrocarbons from CO and H₂ in the presence of metalcatalysts, including carbonyl iron powder.

WO 07/060186 A1 (BASF AG) teaches processes for preparing olefins fromsynthesis gas using Fischer-Tropsch catalysts in a reaction column.

WO 09/013174 A2 (BASF SE) relates to a process for preparingshort-chain, gaseous olefins by reaction of carbon monoxide withhydrogen in the presence of an iron-comprising heterogeneous catalyst,with carbonyl iron powder having spherical primary particles being usedas catalyst.

The EP application No. 08164085.6 (BASF SE) of Sep. 10, 2008 describesan integrated process in which pure carbonyl iron powder (CIP) isprepared by decomposition of pure iron pentacarbonyl (IPC) in a plant A,carbon monoxide (CO) liberated in the decomposition of the IPC is usedfor preparing further CIP from iron in plant A or is fed to anassociated plant B for producing synthesis gas or is fed to anassociated plant C for preparing hydrocarbons from synthesis gas,

and the CIP prepared in plant A is used as catalyst or catalystcomponent in an associated plant C for preparing hydrocarbons fromsynthesis gas from plant B.

Two parallel European patent applications having the same filing date(all BASF SE) relate to particular iron-comprising heterogeneouscatalysts and their use in processes for preparing olefins by reactionof carbon monoxide with hydrogen.

BRIEF SUMMARY OF THE INVENTION

It was an object of the present invention to circumvent disadvantages ofthe prior art and discover an improved catalyst and an improvedeconomical process for preparing olefins. The process should, inparticular, give lower olefins (e.g. C2-C6-olefins, in particularC2-C4-olefins), in particular ethene, propene and 1-butene, veryselectively with at the same time very low formation of methane, carbondioxide, alkanes (e.g. C2-C6-alkanes, in particular C2-C4-alkanes) andhigher hydrocarbons, i.e. hydrocarbons having, for example, seven ormore carbon atoms (C7+ fraction), in particular five or more carbonatoms (C5+ fraction). Constituents of the catalyst should not bevolatile under the reaction conditions.

The catalyst should display an improved operating life and increasedmechanical stability. The increased stability is particularlyadvantageous when the catalyst is used in a fluidized bed or in slurryreactors or else in bubble columns.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 show scanning electron micrographs of preferred carbonyl ironpowder having spherical primary particles before the hydrogen treatmentaccording to step II in the disclosure.

FIGS. 4-5 show, by way of example, agglomerates obtained after thehydrogen treatment.

FIG. 6 shows a carbonyl iron powder obtained in steps IV in thedisclosure.

FIG. 7 show the pore distribution after step II and after step IV.

According to the invention, the following aspects, inter glia, have beenrecognized:

The metallic secondary particles formed in step II with at least partialagglomeration, particularly in a fluidizable fraction having particlediameters in the range from 10 to 250 μm (see below), are, owing totheir chemical composition, ideal catalyst precursors for the synthesisof lower olefins from CO-rich synthesis gases. An additional advantageis the low surface area of the particles, which is preferably below 2m²/g (see below).

A particular advantage is the low oxygen content of the metallicsecondary particles, as a result of which a reduction, and thusactivation of the catalyst, is greatly simplified.

Owing to the method of production, the secondary particles compriseinterstitial pores (intraparticulate pores=pores between the sphericalprimary particles; see FIGS. 5 and 7) which display disadvantageousphysical properties under the synthesis conditions for the lowerhydrocarbons (HCs):

-   -   1) carbon deposits can be formed in the pores and lead to        mechanical rupture of the particles (adverse for operating life,        discharge of fines from fluidized bed)    -   2) the pores promote the formation of undesirable long-chain HCs    -   3) the pores promote the hydrogenation of olefins

The agglomerates (=secondary particles) are, according to the invention,brought into contact with Fe(CO)₅ in a step following theabove-described reduction and the pores are filled with Fe(CO)₅, inparticular by condensation/flooding. Subsequent thermal decomposition ofthe IPC leads to at least predominantly pore- and void-free secondaryparticles which no longer have the adverse properties indicated inpoints 1-3 above and thus significantly increase the absolute yield ofolefins and also the catalyst operating life (chemical and mechanicalaspects, see FIGS. 6 and 7). In addition, the filling of the poresincreases the mechanical stability of the secondary particles.

We have accordingly found an iron-comprising heterogeneous catalyst anda process for producing it, which comprises the following steps:

-   -   I. thermal decomposition of gaseous iron pentacarbonyl to give        carbonyl iron powder having spherical primary particles,    -   II. treatment of carbonyl iron powder obtained in step I with        hydrogen, resulting in the metallic spherical primary particles        at least partially agglomerating,    -   III. contacting of the agglomerates (=secondary particles) with        iron pentacarbonyl,    -   IV. thermal decomposition of the iron pentacarbonyl applied in        step III to give at least predominantly pore- and void-free        secondary particles.

Furthermore, we have accordingly found a process for preparing olefinsby reaction of carbon monoxide with hydrogen in the presence of acatalyst, wherein the abovementioned iron-comprising heterogeneouscatalyst is used as catalyst.

The proportion of spherical primary particles comprised in the carbonyliron powder obtained in step I is preferably >90% by weight, inparticular >95% by weight, very particularly preferably >98% by weight.

The spherical primary particles obtained in step I preferably have adiameter in the range from 0.01 to 50 μm, in particular in the rangefrom 0.1 to 20 μm, very particularly preferably in the range from 0.5 to15 μm, more particularly in the range from 0.7 to 10 μm, moreparticularly in the range from 1 to 10 μm.

The iron content of the spherical primary particles is preferably >97%by weight, particularly preferably ≧99% by weight, in particular ≧99.5%by weight.

The iron is preferably present in its most thermodynamically stablemodification (alpha-iron).

The spherical primary particles are preferably free of pores.

The carbonyl iron powder has, in particular, no thread-like primaryparticles in addition to the spherical primary particles, in particularnot the iron whiskers disclosed in DE 29 19 921 A1 and “Fachberichte fürOberflächentechnik”, July/August 1970, pages 145 to 150 (see above).

FIGS. 1 to 3 show scanning electron micrographs of preferred carbonyliron powder having spherical primary particles before the hydrogentreatment in step II.

Carbonyl iron powder having spherical primary particles which can beused in the process of the invention can be obtained, for example, underthe name “Carbonyleisenpulver CN” from BASF AG or now BASF SE, D-67056Ludwigshafen.

The carbonyl iron powder having spherical primary particles is obtainedby thermal decomposition of gaseous iron pentacarbonyl (Fe[CO]₅), whichhas preferably been purified beforehand by distillation.

The product obtained in step I is treated with hydrogen in step II. Thistreatment of the primary particles with hydrogen is preferably carriedout at a temperature in the range from 300 to 600° C. This treatmentreduces the residual content of carbon, nitrogen and also oxygen in theCIP. (DE 528 463 C1, 1927). Here, the spherical primary particles are atleast partially agglomerated, e.g. to an extent of from 25 to 95% byweight.

The metallic secondary particles formed by at least partialagglomeration in step II preferably have particle diameters in the rangefrom 10 to 250 μm, particularly preferably from 50 to 150 μm. Suchfluidizable particle fractions can be obtained by appropriate sieving.

In step II, metallic secondary particles having BET surface areas (DINISO 9277) of preferably less than 2 m²/g, in particular from 0.2 to 1.9m²/g, are formed.

FIGS. 4 and 5 show, by way of example, agglomerates obtained after thehydrogen treatment.

In step III, the agglomerates are preferably brought into contact withliquid or gaseous iron pentacarbonyl. Particular preference is given toliquid iron pentacarbonyl.

For this purpose, the metallic secondary particles are, for example,introduced into an argon-blanketed vessel and dried at elevatedtemperature, e.g. from 70 to 150° C., in particular, for example, at aninternal temperature in the vessel of 105° C.

Iron pentacarbonyl is then introduced in liquid form a little at a time(e.g. 5% by volume based on the amount of carbonyl iron powder), e.g.through an inlet tube.

The alternative contacting with gaseous iron pentacarbonyl can, forexample, be carried out in a fluidized bed, in particular at atemperature in the range from 120 to 175° C. It is preferably carriedout at an IPC partial pressure (absolute) in the range from 0.7 to 1bar.

The thermal decomposition of iron pentacarbonyl in step IV is preferablycarried out at a temperature in the range from 150 to 350° C., inparticular in the range from 150 to 200° C.

For example, the vessel in which the material from step III is presentis heated to an internal temperature in the range of preferably from 150to 180° C. and the decomposition reaction of the applied IPC ispreferably monitored by means of an IR spectrometer. When the CO contentof the offgas has passed its maximum, the vessel is cooled back down to,for example, 105° C.

Depending on the desired degree of fill of the pores, the procedure ofthe two steps III and IV is repeated.

Predominantly pore- and void-free secondary particles are obtained instep IV. The secondary particles obtained in step II have interstitialpores between the spherical primary particles (pore diameter, inparticular, <4000 nm). The interstitial pores, in particular theinterstitial pores having diameters of <4000 nm, thus represent theabove-described intraparticulate pores (FIGS. 5 and 7) while themeasured pores having diameters of, in particular, >4000 nm can beinterpreted as interparticulate pores (resulting from the interstitialvolume of the secondary particles).

The treatment according to the invention of the secondary particles withiron pentacarbonyl makes it possible to fill the interstitial poresbetween the spherical primary particles, in particular those havingdiameters in the range <4000 nm. This therefore gives predominantlypore- and void-free secondary particles in which, in particular, thedifferential pore volume associated with pore diameters in the range<4000 nm contributes <10%, in a particular embodiment <5%, to themeasured integrated pore volume of the secondary particles.

The amount of iron pentacarbonyl necessary for filling the pores havinga diameter of, in particular, <4000 nm is preferably determined by meansof pore volume measurement by means of mercury porosimetry (DIN 66133).

Particles obtained in step IV are shown, by way of example, in FIG. 6.

Even without any additives, the iron-comprising heterogeneous catalystof the invention displays an advantageous catalytic activity.

In a particular embodiment, an additional step V in which the particlesfrom step IV are doped with a promoter or a plurality of promoters toincrease the catalytic activity is carried out in the production of thecatalyst.

Promotors in iron catalysts for Fischer-Tropsch syntheses are described,for example, in M. Janardanarao, Ind. Eng. Chem. Res. 1990, 29, pages1735 to 1753, or C. D. Frohning et al. in “Chemierohstoffe aus Kohle”,1977, pages 219 to 299.

As suitable promoters, the catalyst can comprise, for example, one ormore of the elements potassium, vanadium, copper, nickel, cobalt,manganese, chromium, zinc, silver, gold, calcium, sodium, lithium,cesium, platinum, palladium, ruthenium, sulfur, in each case inelemental form (oxidation state =0) or in ionic form (oxidation state≠0).

The total doping (i.e. sum of all promoters, if there are a plurality ofpromoters) is preferably in the range from 0.01 to 30% by weight,particularly preferably from 0.01 to 20% by weight, very particularlypreferably from 0.1 to 15% by weight, e.g. from 0.2 to 10% by weight, inparticular from 0.3 to 8% by weight (in each case calculated as elementin the oxidation state 0 and in each case based on iron).

In a particular embodiment of the process of the invention, doping withpotassium ions and/or sodium ions as promoter is carried out in step V.

In a further particular embodiment of the process of the invention,doping with manganese and/or copper, in each case in elemental form orin ionic form, is carried out in step V, especially in addition todoping with potassium ions and/or sodium ions.

Particular preference is given to carrying out doping with a total inthe range from 0.01 to 10% by weight, preferably from 0.1 to 5% byweight, of potassium ions and/or sodium ions (in each case calculated aselement in the oxidation state 0 and in each case based on iron) in stepV.

Particular preference is given to carrying out doping with a total inthe range from 0.01 to 10% by weight, preferably from 0.1 to 5% byweight, of manganese and/or copper (in each case calculated as elementin the oxidation state 0 and in each case based on iron) in step V.

The application of the promoters mentioned can, in particular, beeffected by impregnating the particles with aqueous salt solutions ofthe metals mentioned, preferably carbonates, acetates, chlorides,nitrates or oxides.

In a particular embodiment, compounds which reduce the surface tensionof the impregnation solution, e.g. surfactants, can be added to theaqueous salt solutions.

Furthermore, the elements acting as promoter can be applied by thermaldecomposition of the corresponding gaseous carbonyl compounds, e.g.chromium, cobalt, manganese or nickel carbonyls.

The catalyst of the invention is particularly preferably not applied toa support material.

In the process of the invention, the doped or undoped, iron-comprisingheterogeneous catalyst can be used in the form of pellets.

The pellets are obtained by methods known to those skilled in the art.Preferred shapes of the pellets are tablets and rings.

The pellets can also be comminuted again, e.g. by milling, before beingused in the process of the invention.

The catalyst can be converted into a more synthesis-active state bytreatment with hydrogen and/or carbon monoxide at elevated temperature,in particular at temperatures above 300° C., before being used in theprocess of the invention. However, this additional activation is notabsolutely necessary.

In the process of the invention, the starting materials carbon monoxideand hydrogen are preferably used in the form of synthesis gas.

The synthesis gas can be produced by generally known methods (asdescribed, for example, in Weissermel et al., Industrial OrganicChemistry, Wiley-VCH, Weinheim, 2003, pages 15 to 24), for example byreaction of coal or methane with hydrogen or by partial oxidation ofmethane. The synthesis gas preferably has a molar ratio of carbonmonoxide to hydrogen in the range from 3:1 to 1:3. Particular preferenceis given to using a synthesis gas which has a molar mixing ratio ofcarbon monoxide to hydrogen in the range from 2:1 to 1:2.

In a particular embodiment of the process of the invention, thesynthesis gas comprises carbon dioxide (CO₂). The CO₂ content ispreferably in the range from 1 to 50% by weight.

The process of the invention is preferably carried out at a temperaturein the range from 200 to 500° C., in particular from 300 to 400° C.

The absolute pressure is preferably in the range from 1 to 100 bar, inparticular from 5 to 50 bar.

The WHSV (weight hourly space velocity) is preferably in the range from50 to 10 000, particularly preferably from 150 to 5000, parts by volumeof feed stream per unit mass of catalyst and hour (l/kg●h). f

Preferred reactors for carrying out the process of the invention are:fluidized-bed reactor, fixed-bed reactor, suspension reactor,microreactor.

In a fluidized-bed reactor, microreactor and suspension reactor, thecatalyst is preferably used in powder form.

The powder can also be obtained by milling previously formed pellets.

In a fixed-bed reactor, the catalyst is used as shaped bodies,preferably in the form of pellets.

The use of such reactors for the Fischer-Tropsch synthesis is described,for example, in C. D. Frohning et al. in “Chemierohstoffe aus Kohle”,1977, pages 219 to 299, or B. H. Davis, Topics in Catalysis, 2005, 32(3-4), pages 143 to 168.

The process of the invention gives a product mixture comprising olefinswith an olefin carbon selectivity, in particular an α-olefin carbonselectivity, for the C2-C4 range of preferably at least 20%, e.g. in therange from 20 to 30%. In the selectivity figures, carbon dioxide formedis not taken into account (i.e. excluding CO₂).

In a particular embodiment, a product mixture comprising olefins havingan olefin carbon selectivity for the C2-C4 range of at least 20%, e.g.in the range from 20 to 30%, with at least 90% of this at least 20% inturn being made up by ethene, propene, 1-butene, is obtained. In theselectivity figures, carbon dioxide formed is not taken into account(i.e. excluding CO₂).

In a particularly preferred embodiment, a product mixture comprisingolefins having an olefin carbon selectivity for the C2-C4 range of atleast 25%, e.g. in the range from 25 to 30%, with at least 90% of thisat least 25% in turn being made up by ethene, propene, 1-butene, isobtained. In the selectivity figures, carbon dioxide formed is not takeninto account (i.e. excluding CO₂).

The olefins obtained are used, for example, in processes for preparingpolyolefins, epoxides, oxo products, acrylonitriles, acrolein, styrene.See also: Weissermel et al., Industrial Organic Chemistry, Wiley-VCH,Weinheim, 2003, pages 145 to 192 and 267 to 312.

All pressures indicated are absolute pressures.

EXAMPLES Catalyst Production Example 1 (According to the Invention)

Filling of the pores of pure, agglomerated carbonyl iron powder(secondary particles) from step II with iron pentacarbonyl as per stepIII and IV.

The amount of iron pentacarbonyl necessary for filling the pores havinga diameter of, in particular, <4000 nm was determined by means ofmercury porosimetry (DIN 66133).

200 ml of carbonyl iron material having a particle size distribution ofthe secondary particles such that 90% by weight have a diameter in therange from 50 to 100 μm, see FIG. 4, were produced from carbonyl ironpowder grade CN, BASF AG or now BASF SE, by treatment with hydrogen atat least 300° C. The carbonyl iron material was dried at 105° C. for 5hours under an argon atmosphere in a stirred vessel. 10 ml of ironpentacarbonyl were then introduced. The vessel was subsequently heatedto an internal temperature of about 165° C. The decomposition wascarried out at 165° C. with stirring of the particles. The reaction wascomplete when no iron pentacarbonyl and no free carbon monoxide weredetected in the offgas stream. These steps were repeated 13 times. Afterthe synthesis was complete, the product was flushed with argon at 100°C. for at least 12 hours until the CO and Fe(C0)₅ content in the offgaswas <0.1 ppm by volume.

Example 2 (According to the Invention)

Production of K- and Cu-Doped, Filled Carbonyl Iron Catalyst byImpregnation of the Catalyst From Example 1

50 g of catalyst were produced as described in example 1 and impregnatedwith 5.5 ml of aqueous potassium/copper nitrate solution under ambientconditions (room temperature, atmospheric pressure). The aqueouspotassium/copper nitrate solution was produced by dissolving 1.93 g ofcopper nitrate trihydrate (>99.5%, Merck) and 0.26 g of potassiumnitrate (99%, Riedel de Haen) in 5.5 ml of demineralized water. Theimpregnated catalyst was dried at 120° C. for 4 hours. The catalystobtained comprised 0.18% by weight of K and 0.88% by weight of Cu.

Example 3 (Comparative Catalyst)

Carbonyl iron material having a particle size distribution of thesecondary particles such that 90% by weight have a diameter in the rangefrom 50 to 100 μm, see FIG. 4, produced as described in example 1. Thismaterial was not after-treated with iron pentacarbonyl.

Performance of the catalysts according to the invention (examples 1, 2)and the comparative catalyst (example 3) in the process of the inventionwith prior identical activation

Example 4

A series of comparative performance tests was carried out using, in eachcase, about 2.0 g of catalyst from one of examples 1, 2 and 3 and inertmaterial dilution (catalyst: alpha-aluminum oxide=1:3 (weight ratio)).The catalysts were introduced into a fixed-bed reactor and started updirectly using synthesis gas (H₂:CO=1:0.9 (molar)) at a rate of about2.1 standard l/h at 25 bar in the reactor at 340° C. As internalstandard for the on-line GC analysis, an additional 0.1 standard I/h ofnitrogen gas was introduced. The results of the experiments carried outover a period of at least 100 h are shown below for the respectivecatalyst systems.

(standard l=standard liters=volume converted to STP).

Catalyst Example 1 Example 2 Example 3 % max. CO conversion 98 98 98Time to conversion of >95% [h] 35 6 56 % of carbon in C₇₊ 30 28 36 % ofcarbon in carbon 13 8 18 deposits, without CO₂

In the selectivity figures in the examples, carbon dioxide formed is nottaken into account (i.e. without CO₂).

The measured values for example 4 shown in the table make it clear thatthe desired improvements compared to the comparative catalyst (example3) are achieved by filling the pores <4000 nm in the secondary particleswith iron pentacarbonyl (example 1). Thus, both the formation oflong-chain hydrocarbons (C7+) and the formation of carbon deposits aresignificantly reduced.

In addition, the activity can be significantly increased byafter-impregnation with K/Cu salts (catalyst from example 2).

Analysis of the reaction products:

The product streams were sampled via heated stream selectors and linesafter condensing out the long-chain hydrocarbons in a hot separator(about 160° C., 25 bar) and fed to an on-line gas chromatograph (GC).

GC: Agilent 6890N with FID and thermal conductivity detector.

Precolumns: CP-Poraplot Q, length 12.5 m, ID 0.53 mm, film thickness 20μm

FID:

Injector 250° C., split ratio 50:1, carrier gas helium, column DurabondDB-1 (length 60 m, ID 0.32 mm, film thickness 3 μm), detector 280° C.

Thermal conductivity detector:

Injector 200° C., split ratio 10:1, carrier gas argon, column Carboxen1010 (length 30 m, ID 0.53 mm), detector 210° C.

Temperature program: 40° C.-5 min—7° C./min—250° C.-5 min, carriergas:helium.

FIGS. 1 to 3:

Carbonyl iron powder (CIP) having spherical primary particles which canbe used according to the invention in step II

The invention claimed is:
 1. A process for producing an iron-comprisingheterogeneous catalyst, which comprises the following steps: I. thermaldecomposition of gaseous iron pentacarbonyl to give carbonyl iron powderhaving spherical primary particles, II. treatment of carbonyl ironpowder obtained in step I with hydrogen, resulting in the metallicspherical primary particles at least partially forming agglomerates,III. contacting the agglomerates with iron pentacarbonyl, and IV.thermal decomposition of the iron pentacarbonyl applied in step III togive at least predominantly pore-free and void-free secondary particles.2. The process according to claim 1, wherein the agglomerates arebrought into contact with liquid or gaseous iron pentacarbonyl in stepIII.
 3. The process according to claim 1, wherein the thermaldecomposition of the iron pentacarbonyl in step IV is carried out at atemperature in the range from 150 to 350° C.
 4. The process according toclaim 1, wherein the spherical primary particles obtained in step I havea diameter in the range from 0.01 to 50 μm.
 5. The process according toclaim 1, wherein the primary particles obtained in step I have an ironcontent of greater than 97% by weight.
 6. The process according to claim1, wherein the primary particles obtained in step I are pore-free. 7.The process according to claim 1, wherein the carbonyl iron powderobtained in step I does not comprise any thread-like primary particles.8. The process according to claim 1, which further comprises thefollowing step: V. doping of the secondary particles from step IV withthe elements potassium, vanadium, copper, nickel, cobalt, manganese,chromium, zinc, silver, gold, calcium, sodium, lithium, cesium,platinum, palladium, ruthenium and/or sulfur, in each case in elementalform or in ionic form.
 9. The process according to claim 8, wherein thetotal doping is in the range from 0.01 to 30% by weight (based on iron).10. The process according to claim 8, wherein doping with a total in therange from 0.01 to 10% by weight (based on iron) of potassium ionsand/or sodium ions is carried out in step V.
 11. The process accordingto claim 8, wherein doping with a total in the range from 0.01 to 10% byweight (based on iron) of manganese and/or copper, in each case inelemental form or in ionic form, is carried out in step V.
 12. Theprocess according to claim 1, wherein the secondary particles used instep III have a diameter in the range from 10 to 250 μm.
 13. Aniron-comprising heterogeneous catalyst which can be obtained by aprocess according to claim 1.